The US-based Institute for Science and International Security (ISIS) has said it agrees with the assessment of France’s Nuclear Safety Authority (ASN) that the incident at Fukushima should be classified as level 6 on the International Nuclear Event Scale (INES), one below Chernobyl.

Following a number of explosions and a fire at the plant which released dangerous levels of radiation, ISIS said the situation had “worsened considerably” and was now closer to a level 6 event. “It may unfortunately reach a level 7,” it added.